Needled textile fabrics are normally composed of synthetic organic textile fibers, e.g. polyester, needled together into a consolidated mat. While such fabrics may also be made of natural organic fibers, e.g. cotton, these natural fibers are capable of being formed into a non-woven fabric of substantial properties by the more traditional process, e.g. felting, and hence, are not usually needled to form a non-woven fabric. Inorganic fibers, on the other hand, such as glass fibers, are not normally either felted or needled, but are consolidated into a fabric of, generally, low physical properties by an air lay or wet lay process. This is because inorganic fibers, by virtue of the materials and process of producing, have very little crimp therein, are of high modulus and substantially brittle, all of which do not lend the inorganic fibers to being either carded, needled or felted. U. S. Pat. No. 3,608,166, for example, details the difficulties in needling glass fibers. Limited needling has been done, however, for the purpose of lightly tacking a glass fiber batt. U.S. Pat. No. 3,338,777 teaches that the ability to needle glass fibers can be improved by crimping those fibers, but this is quite unacceptable from a commercial point of view because of the cost thereof.
Thus, most needled fabrics, being composed generally of organic fibers, find a variety of applications where relatively high physical properties are required, e.g. high strengths, with substantially uniform physical properties in both the longitudinal and transverse directions, and particularly in those applications where economics dictate the use of materials less expensive than woven fabrics or where the applications require more uniform thickness direction properties than can be provided by woven fabrics, e.g. as a heat insulator. However, since such needled fabrics are generally restricted to organic fibers, as noted above, the application of these needled fabrics has been substantially limited when higher temperatures are involved, especially where heat insulators are intended. Where heat insulators are intended, the art has been generally unsuccessful in providing needle fabric which will withstand such higher temperature, since the organic fibers of the needled fabrics have too low a softening temperature.
The art has attempted to overcome this difficulty by use of a number of different approaches. In one approach, as exemplified by U.S. Pat. No. 3,338,777, organic fibers and glass fibers are mixed. Such mixture of fibers significantly improves the ability to needle the glass fibers into a consolidated fabric of reasonable physical properties and improves the heat resistance of the fabric. However, this approach suffers from the disadvantage that the mixture of organic fibers and glass fibers decreases the resulting physical properties of the resulting fabric, as opposed to an all organic fiber fabric, due to the increased difficulty of needling the glass fibers into a fabric of high strengths. Further, the organic fibers mixed with glass fibers reduced the insulating properties of the glass fibers.
Aside from the foregoing difficulties in resulting properties, a needled mixture of organic fibers and glass fibers has recently been determined to have a most undesired health problem. In needling the mixture, glass fibers may be disposed throughout the thickness of the needled fabric, and including the surfaces thereof. The co-needling of the organic fibers and glass fibers, nevertheless, breaks many of the low stretchable and brittle glass fibers. These very small broken glass fibers are easily displaceable from the surface of the fabric when the fabric is in use and the displaced and broken (as well as unbroken) glass fibers will freely float in the air. If workers inhale these broken glass fibers, serious lung damage can result. Accordingly, for safety sake, use of such fabrics in considerably discouraged, or even prohibited, in many industries.
An attempt at a different approach is disclosed in U.S. Pat. No. 3,608,166, where organic fibers are used to needle "connecting" fibers through a glass fiber mat, preferably reinforced with a woven fabric, but that patent recommends oiling the glass fibers to avoid the problem of breakage and teaches using only about 12 to 15 needle punches per square centimeter. This is an unacceptably low number of needle punches and the resulting needled mat has low strengths.
U.S. Pat. No. 3,975,565 acknowledges that inorganic fibers are difficult to needle due to the relatively low stretch properties and brittleness of those fibers but goes on to disclose that it was found that inorganic fibers could be satisfactorily needled into a fabric by needle punching a combination of a mat of inorganic fibers and a web of organic fibers when the web of organic fibers is of a small thickness compared to the thickness of the mat of the inorganic fibers. During the needling process, the organic fibers are needled into the body of the mat of inorganic fibers and therefore hold the mat of inorganic fibers to the thin web of organic fibers. This provides a layered product with one layer being that of the inorganic fibers and one thin layer being that of the organic fibers. Thus, the properties of the layer of the inorganic fibers are substantially retained, and the layer of the organic fibers serves to hold the layer of inorganic fibers in place. This approach, therefore, offered the promise of a solution to one of the problems in the art, as identified above.
However, that approach suffers from a decided disadvantage. In practice, it was found that in needling the organic fiber layer to the inorganic fiber layer, needle punches of more than 260 punches per square inch could not be tolerated, since otherwise damage to the inorganic fibers occurred and that with needle punches of more than 260 per square inch, inorganic fiber damage resulted in more than a 25% loss of the inorganic fiber layer strength. Such a low number of needle punches per square inch is not capable of producing acceptable overall physical properties of the composite. In addition, the considerable breakage, during needling, of the inorganic fibers constitutes a very definite health hazard, as explained above in connection with the needled combination of organic fibers and glass fibers.
In U.S. Pat. No. 4,522,876, which is of common inventorship and ownership herewith, the entire disclosure of which is incorporated herein by reference, it is disclosed that a needled fabric may be prepared by needling a composite batt prepared from a glass fiber batt and an organic fiber batt, where the needling takes place from at least the side of the composite batt having the organic fiber batt. The needling must be carried out in a manner such that the glass fibers of the glass fiber batt are not substantially engaged by the barbs of the needles during the needling operation. With such lack of engagement, the needles can stitch organic fibers from the organic fiber batt into and through the glass fiber batt so as to bind the organic fiber batt to the glass fiber batt, while at the same time not substantially engaging, and, hence, breaking or displacing the glass fibers of the glass fiber batt. Stated another way, the needling is carried out in such a manner that the fibers of the organic fiber batt are needled into the glass fiber batt while the fibers of the glass fiber batt are left substantially undisturbed. By such a needling technique, almost any numbers of needle punches may be used in the process to form either a lightly needled or a highly needled organic fiber layer while at the same time not breaking or displacing the glass fibers of the glass fiber batt.
The resulting composite fabric has good physical properties due to the amount of needling of the organic fiber layer. Also with such needling, the stitching o the organic fibers into and through the glass fiber batt will so bind the glass fiber layer and the organic fiber batt that they are essentially nondetachable, one from the other. Even further, since such needling will not substantially displace glass fibers from the glass fiber batt into the organic fiber layer, the resulting needled organic fiber layer will be essentially free, at least on the outer surface thereof, of glass fibers. Thus, that surface avoids the health problem described above. Further, if the glass fiber batt is sandwiched between two organic fiber batts, and a similar needling takes place, from one or both sides of the sandwich, then again the resulting sandwiching organic fiber layers will not have glass fibers therein, at least on the outer surfaces thereof, and the entire resulting fabric will not pose the health problem described above.
The product of the aforenoted U.S. Pat. No. 4,522,876 has found wide acceptance. For example, it is used an insulator over the floorboard in the area of the catalytic converter and underneath the carpet of automobiles and trucks, in order to reduce the temperature of the carpet under the feet the passengers in such a vehicle. As disclosed in that patent, such an insulator is particularly advantageous, in that it can be easily assembled in producing the vehicle, without the health hazards noted above, while at the same time providing excellent insulation to the area of the floorboard over the catalytic converter. In practice, the insulating fabric of the aforementioned patent is attached to the material which is placed between the floorboard and the carpet of the vehicle so that the insulating fabric is strategically positioned over the catalytic converter, which is normally under the floorboard of the vehicle. The material placed between the floorboard and the carpet can be of a variety of materials, but very often that material is a non-woven product referred to as "shoddy" material, which is a felted material of waste fibers. The carpet, shoddy material and insulator are preassembled, as a one-piece unit, usually by a heat activated glue and press operation. Thus, when the unit is placed over the floorboard, the carpet, shoddy material and insulating fabric of the aforementioned patent are automatically placed at the correct position of the floorboard so that the insulating fabric is placed over the higher temperature of the floorboard generated by the catalytic converter thereunderneath. This considerably facilitates assembly of the carpet in the vehicle, since the insulating fabric of the aforementioned patent will automatically be placed in the correct position when the unit is placed over the floorboard. Sometimes, additional shoddy material is laid underneath the shoddy material, but not under the insulating fabric, in order to avoid any overall variations in thickness of the carpet as installed on the vehicle. The additional shoddy material may be feathered toward the edges of the carpet in order to make a smooth appearance.
While this is a very acceptable and widely used application of the insulating fabric of the aforementioned patent, it has now been discovered that there are certain difficulties associated therewith, especially in regard to certain installations in certain vehicles. In this regard, certain vehicles have areas of higher temperatures at the floorboard which are either more extensive than the areas immediately above the catalytic converter, or, in some cases, even areas which are spaced apart. For example, in many trucks, the exhaust pipes, at least in part, pass through the tunnel area of the floorboard and the area of the floorboard adjacent to those exhaust pipes can be heated to relatively high temperatures Thus, while the application of the insulating fabric of the aforementioned patent, as described above, can keep the temperature of the carpet under the feet of a passenger to acceptable limits in regard to the area over the catalytic converter, the other higher temperature areas, such as portions of the tunnel, can cause uncomfortable temperatures to the passengers of the truck. Further, when extended areas or multiple areas experience higher temperatures, the combined higher temperatures of these areas can make large sections of the floorboard uncomfortable for passengers.
Of course, multiple sections of the insulating fabric of the aforementioned patent could be strategically hand placed on the shoddy material for covering most of these extended areas of higher temperature, even when those extended areas are spaced apart, but this would considerably increase the hand labor cost of strategically placing the insulating fabric of the foregoing patent on the shoddy material. Further, it has been found that in certain vehicles, especially trucks, the temperature of the floorboard in localized areas is quite high, and the insulating fabric of the aforementioned patent is not sufficient, in the usual thicknesses produced, to adequately insulate those higher temperature areas. Of course, the insulating fabric of the aforementioned patent could simply be increased in thickness to achieve greater insulation, but this would result in substantial increases in the cost of that insulating fabric.
It would, therefore, be a substantial advantage to the art to provide a fabric which is capable of insulating higher temperature portions of the floorboard while at the same time providing that fabric such that unnecessary insulation is not used on areas of the floorboard which do not experience those higher temperatures.